It is known in the manufacture of motor vehicles to hydroform tubular structures such as roof rails and frame rails that are made from lengths of tube having open ends. The length of tube is captured with the die cavity of a hydroforming die, seals are applied to seal the open ends of the tube, and pressurized fluid is introduced through the tube seals to expand the tube into a shape defined by the die cavity.
It would be desirable to enable improvements in the manufacture and hydroforming of ring-shaped structures of the type that are used in vehicle body applications such as radiator supports, engine cradles, and door openings for the side doors and rear hatch closures.